1. Field of the Invention
The invention is directed to an improvement in vacuum devices. More particularly the invention is directed to an improvement in bell jars which have an open bottom with a planar rim thereabout and which fit against a flat surface with a gasket between the planar rim and the surface. Such arrangements find particular application in vacuum deposition apparatus and in other vacuum manufacturing apparatus.
2. Prior Art
The prior art has used L-shaped elastomeric rings to seal the rim of a bell jar or the like to a flat surface. The term L-shaped ring is used to denote rings having an L-shaped cross-section. These L-shaped rings have generally been clamped in place with what amounts to oversized hose clamps or have occassionally been taped in place. One leg of the L-shaped rings has been clamped generally against the outside of the bell jar while the other generally shorter leg of the L-shaped ring has been in contact with the bottom rim of the bell jar. The hose clamp type arrangement has generally been placed around the longer leg of the L-shaped ring. The bell jar has then been propelled against a flat surface in the usual manner to ensure vacuum tight fit and the inside of the bell jar has been evacuated in a conventional manner.
A serious problem exists when such L-shaped rings are used to seal the bottoms of bell jars to flat surfaces. Most particularly, this problem consists of a creeping of the L-shaped ring upwardly within the hose clamp or tape and away from the bottom rim of the bell jar. This has required frequent replacement of bell jar sealing rings. The present invention provides a creep resistant sealing arrangement for bell jars and the like. Most particularly, this arrangement comprises a unitary resilient elastomeric ring having a generally J-shaped cross-section rather than a generally L-shaped cross-section. The arrangement further includes means for fastening the generally longer outer leg of the J-shaped ring inwardly against the outside of the bell jar. The inner generally shorter leg of the J-shaped ring serves to bind against the inside of the bell jar thus preventing the J-shaped ring from creeping out from under the fastening means which would generally comprise a metal band such as a large hose clamp or the like while keeping out-gassing of the J-shaped ring minimal. As a result of the significantly improved creep resistance of the sealing arrangement of the present invention, replacement of elastomeric rings, in the case of the present invention elastomeric rings having a J-shaped cross-section, is significantly reduced and down-time of the vacuum apparatus is also significantly reduced.